The present invention relates to an arrangement for treating solids settled on the bottom of an electrolytic tank.
In electrolytic processes, metals such as copper, nickel and zinc, are precipitated on the surfaces of cathodes located in the electrolytic tank, starting either with metal anodes that are dissolved into the electrolyte present in the electrolytic tank, or with metal ions that are already dissolved into the electrolyte. However, all solids are not precipitated onto the cathode surfaces, for example precious metals and solid impurities present in the electrolyte. Therefore on the bottom of electrolytic tanks, there are accumulated, along with the metal refining process, various solids that must from time to time be removed from the tank, for instance because said solids contain valuable ingredients, such as precious metals, or because a thicker solids accretion threatens the purity of the cathode obtained from the electrolytic process.
Usually the solids accumulated in the electrolytic tank are at least partly very finely divided and only somewhat heavier than the electrolyte, wherefore it is difficult to separate the solids from the electrolyte. During the electrolytic process, the circulation of the solids from off the bottom of the electrolytic tank is very harmful, because in that case there is a particularly high risk that the solids proceed onto the cathode, and this would essentially weaken the purity of the metal to be produced.
The removal of the solids accumulated on the bottom of an electrolytic tank usually requires that the whole electrolytic process must be interrupted, which reduces the efficiency per time, i.e. the productivity of the electrolytic plant. Hence the removal of solids must be arranged so that it forms part of the process of replacing the electrodes, i.e. anodes and cathodes; this, however makes the replacement process complicated and slow, and also restricts the removal of solids to take place in the rhythm dictated by the process of replacement. Moreover, a remarkable amount of the electrolyte must be first removed from the tank and then fed back therein, which generally leads to harmful effects in the electrolyte quality and causes a lot of extra work. Into the solids treatment system, there also flows a remarkable amount of electrolyte, which must be replaced with new and may be harmful in the further treatment of the solids. Moreover, the manual washing of the electrolytic tanks makes the process clearly more labor-intensive and subjects the employees to various health hazards, among others owing to the effects of the ingredients contained in the splashes and spray emanating from the tank. In addition, owing to the personnel required by the washing of the tanks, the automatization of the electrode treatment is often nearly impossible, which further increases the labor demand in an electrolytic plant.
From U.S. Pat. No. 6,299,756, there is known a separating element for separating the bottom part of an electrolytic tank from the rest of the tank space in connection with the removal of the solids settled on the tank bottom. In said publication, in the electrolytic tank there are arranged support and control members that form the trajectory of the separating element, so that the separating element can be placed in the electrolytic tank and removed therefrom through a space provided in between at least one end wall and the electrode placed nearest to said end wall. In the arrangement according to said publication, the separating element is provided with nozzles attached thereto, and through said nozzles, liquid or gas is conducted to the bottom part of the electrolytic tank in order to help remove the solids. The solids and liquid are removed for instance through a discharge aperture provided in the electrolytic tank bottom. However, the solids may contain particles that are coarser than the rest of the material and are not discharged in the manner described above. Owing to their larger size, they also may cause blockages in the outlet channels. Typically the particles with a larger grain size are separated from the finer slurry after the tank cleaning step.
The object of the invention is to realize a completely new type of arrangement to be used for treating the solids settled on the bottom of an electrolytic tank. The invention is characterized by the novel features set forth in the appended claims.
The arrangement according to the invention is characterized in that it comprises a collector element which is moved essentially along the electrolytic tank bottom or in the vicinity thereof, said collector element comprising means for separating coarse particles from the rest of the solids. By means of the arrangement according to the invention, coarse particles can be separated from the rest of the solids already in the electrolytic tank, preferably without having to first drain the electrolyte from the tank. The arrangement can also be used in connection with the cleaning of an already emptied tank.
A preferred embodiment of the arrangement according to the invention is characterized in that the means for separating coarse particles consist of a sieve element. By installing the sieve element in the collector element, there is obtained an advantageous and effective structure for separating and collecting coarse particles.
Another preferred embodiment of the invention is characterized in that in connection with the collector element, there is arranged a lid element, so that the collector element and/or the lid element are movable at least with respect to each other. By providing the collector element with a movable lid arrangement, it can be ensured that the separated coarse particles cannot move from the collector element back to the tank, when the collector element is being removed from the tank.
Another preferred embodiment of the invention is characterized in that the arrangement comprises means for directing a jet of some fluid or intermediate agent to the solids in the collecting direction prior to the collector element. By means of intermediate agent jets, the detaching of the solids from off the tank bottom can be boosted, and their transfer to the collector element as well as the separation of solids by the sieve element and the passage of the finer particles through the sieve can be intensified.
By providing the arrangement according to the invention preferably with at least one suction element arranged in succession to the collector element in the collecting direction, at least an essential part of the finer solids particles that penetrated the sieve element of the collector element are effectively removed from the tank.